A need exists to join thermoplastic components, such as those formed from glass fiber reinforced polypropylene, or the like, to other plastic components formed of similar materials. To date, such joining has been achieved via adhesives, mechanical fasteners, laser welding, sonic welding and/or vibration welding but each of these techniques suffers from disadvantages.
For example, low energy surface adhesives (LESA's) must be employed to adhesively join glass fiber reinforced polypropylene components. LESA's are expensive, typically require long cure times and can produce undesired fumes while they cure. These factors contribute to high manufacturing costs for assemblies joined by LESA's.
The joining of plastic components with mechanical fasteners can result in low strength joints, as the mechanical fasteners only connect the components at specific locations and can incur high labour costs to install. Further, such fasteners can be subject to mechanical failure and can result in failure of the assembly of components.
Laser welding can be employed to join plastic components, but at least one of the components must be at least partially transparent to the Laser energy for the process to work and this limits the type of material, finishes and colors of the components to be joined. Further, Laser welding is a linear process and thus long joints can take significant times to form as the laser must traverse the entire joint length. Further, laser welding techniques can limit the amount of glass fiber which can be added to the thermoplastic material, due to the scattering of the laser energy by the glass fibers and thus the mechanical properties of plastic components joined by laser welding can be unduly limited.
Vibration welding can also be employed to join plastic components but is limited to making planar joints which do not change profile and thus the use of vibration welding is often too limited for many desired assemblies. Sonic welding suffers from similar problems and is typically limited to making relatively short joints and has high associated equipment costs.
More recently, interest has developed in joining plastic components, such as glass fiber reinforced polypropylene components, via resistive implant welding. In this technique, an electrically conductive implant is positioned between the two components to be joined and pressure is applied to the area of the components contacting the implant. An electrical current is then passed through the implant causing it to heat and melt the material of the components adjacent it. The melted portions of the components intermingle under the applied pressure and, when the current is removed and the implant and components cool, a weld is formed between the components. Cycle times for the welding process of much less than a minute can be easily achieved.
While resistive implant welding has offered many advantages over other methods of joining plastic components, it has also suffered from disadvantages in that the placement and retention of the resistive implant between the components to be joined has been difficult to achieve and/or labour intensive.